Analytical method



ANALYTICAL METHOD Casimir J. Munter, Upper St. Clair Township, Allegheny County, Pa., assignor to Hagan Chemicals & Controls, Inc., a corporation of Pennsylvania No Drawing. Filed July 275, 1958, Ser. No. 750,896 5 Claims. c1. zaf-zso f j The present invention relates to a rapid. and efiective method of analyzing steam or water samples to ascertain with accuracy the presence of certain aliphatic amines.

In recent years certain high molecular weight amines and their. salts, often simply called filming amines, have been used extensively to protect the surfaces of pipes and fluid-conveying apparatus in contact with aqueous This corrosive solutions which are corrosive to metals. action is generally caused by carbon dioxide, oxygen, ammonia, or other substances in either a gaseous, vapor, or liquid state, present in the water or steam being transported in the pipes.

The principal application of the amine compounds is in steam generating apparatus. The compounds may be added either to the boiler water where during the conversion of the water to steam, a certain portion of the amine compound is carried over with the steam into the pipes and other conduits which carry the steam to the point of use, or they may be added directly to the steam line by suitable chemical feeding equipment. The addition of the high molecular weight amines and related compounds to the. steam line of a system is described in US. Patent 2,460,259 which issued to Harry Lewis Kahler, while the addition of these compounds to boiler waters is described in US. Patent 2,400,543 which issued to Wayne L. Denman. This second patent was subsequently reissued as Re. 23,614 and re-reissued as Re. 24,473.

The amine compounds which are disclosed in these patents for preventing corrosion in steam systems apparently form a mono-molecular film on metal surfaces. This film protects iron, steel, brass, copper and other metals from corrosion. The amount of corrosion-inhibiting amine compound initially added to either the steam or the boiler is very small, usually in the range of from 1 to parts per million, based on either the steam or boiler water, depending upon the point of introducing the inhibitor. Although larger or smaller amounts may be used, the amine compounds are relatively costly and obviously it is desirable to minimize the concentration for economical operation of the system. Since the amine forms a thin film on the metal surfaces through- .posed by workers in the art but none has proven satisfactory largely because of the very low concentration of amine that is detectable in most instances. amine compounds used are water-insoluble and any titra- Most of the tion method for determining amine in the steam system involves extraction of the amines from the boiler water and/or condensed steam by organic solvents followed by further analytical procedure. This can lead to appreciable error particularly inthe extraction phases ,of the procedure.

2,977,200 Patented Mar. 28, 1961 I have found that the high molecular weight amines,

' and amine salts which are used in practicing the inventions claimed in the Denman and Kahler patents may .be detected even in very-minute amounts by observing a colorchange produced on a metal-dye lake formed in a buffered solution. The color ranges froma golden yellow with no. amine compound present through various gradations of green to a deep blue where 2.5 parts'pe million of the amine compound are detected. V ,I have found that, my method may be applied to' a process using'a lake ofcopper andfAzurol B dye in conjunction with a colorimeter for estimating the amount of amine present. Other metal-dye lakes such as zinc may be used in this method but the combination of the Azurol B dye and copper is by far the most satisfactory.

Reagents Before carrying out my test procedure, I prepared three reagents which I call No. 1, No. 2, and No. 3. They are compounded as follows: 1.

No. 1. 216 ml. of reagent-grade glacial acetic acid (99.5%) are added to about 600 ml. of distilled water in a one liter volumetric flask. The solution is diluted to the one liter mark with distilled water and the flask is agitated to insure complete mixing.

N0. 2. A stock solution of the dye is prepared bydissolving 14 grams of reagent-grade sodium carbonate'and 14 grams of reagent-grade sodiumbicarbonate in about 400 ml. distilled water in a 500ml. volumetric flask. After the carbonates are thoroughly dissolved, 2.58 0 grams of Chromoxane pure Blue BA New CF'dye are added to the solution. This dye is commonly known as azure blue or Azurol B dye. The flask is stoppered and agitated until the dye is completely dissolved. The solution is then diluted to the 500 mark with distilled water. To .convert the stock solution of the dye into the dilute solution employed in the test, 28 grams of regrade sodium bicarbonate are completely dissolved in "about 700 ml. of distilled water in a one liter volumetric flask and exactly 10 ml. of the stock dye solution which has already been prepared is added to the flask and it is further diluted to the one liter mark with distilled water. Reagent No. 2 is now ready for use. p

No. 3. A stock solutionof this reagent is first prepared by adding exactly 1.150 grams of reagent grade cupric sulfate (CuSO,.5H O) and 15.6 ml. of reagentgrade glacial acetic acid (99.5% CH COOH) to about 700 ml. of distilled water in a one liter volumetric flask. The flask is agitated until the solids are completely dissolved and the solution is then diluted to the one liter mark with distilled water. The final reagent is then prepared by further diluting exactly 100 ml. of the pre pared stock solution to one liter with distilled water.

- Sampling Having prepared the reagents, the sampling technique is carried out as follows: t

(1) I add by means of a graduated cylinder 10 mlof reagent No. 1 to a clean 500 ml. Pyrex glass sampling bottle. 4 v

2) The sampling bottle isthen filled to the-bottom-of its neck with the sample to be analyzed. The bottle -is capped and shaken to obtain uniformity of contents. If the sample is hot it should be cooled in the bottle or about ml. of the sample should ,bewithdrawn. and this portion should be cooled in an Erlenmeyer fiaskto F. or less. I

(3) If the sample to be analyzedis'turbid or contains organic coloring matter, 200 to 300ml. of the sample 3 should be. collected in, a separate container for reference purposes. Reagents are not added to this sample.

Analysis To carry out the actual analytical procedure which is the; subject of my invention, I perform the following steps: 7 V v (l) 500 ml. of the cool acidified. sample suspected of containing from v to 2.5 p.p.m. of amine; compound are placed in an Erlenmeyer flask. t (2) From a graduated cylinder 10.0 ml. of reagent No. 2 are added to the Erlenmeyer flask and. the flask is swirled gently for mixing purposes.

(3) From a graduated cylinder 3 are added and mixed. gently.

(4) A conventional viewer containing three viewer tubes is placed in position so that the tops of the tubes point toward a window or other source of light. The outer t'wo tubes are filled to their respective marks with clear tap water or with an actual blank'sarnple if the sample is turbid or contains organic coloring matter. After solution from step 3 has been allowed to stand 20 minutes, the center tube is filled to the mark with this solution. A color slide is placed in the slots so that one of the arrows on the slide is directly below the white arrow on the name plate of the viewer. The sample under observation is compared with the color standards by lookingat the reflections of the three tubes in the mirrorrather than by looking down through thetubes. If the colorof the sample doesnot match either of the standards or does not lie between them, theslide is moved until the next arrow is below the mark on the viewer and the comparison is again made. The amine concentration imparts per million is read from the value of the matching standard.

lncarry ingout my procedure, I preferto' use a viewer sold. by. Hagan Chemicals & Controls, Inc. known as a Hagan Viewer No. 150 because the analytical procedure 100- ofreagent No.

using a viewer is extremely accurate and is preferred where precise determinations are to be made. However, it is possible to eliminate the fourth step, viz. the use of the viewer, and make a visual observation at the conclusion of the third step inthe flask or in standard colorimetric tubes. If'the sample being; observed has a golden yellow color, no filming, amine ispresent. If'a deep blue color develops, the analyst will know that 2.5 ppm. or more of amine is present and the concentration in the 'boileror' the steam line can safely bereduced'for economical operation. In other, words, assuming that a desirable concentration of'amine compound is one part per million, accurate controlcan be maintained by making periodic analysjesandholding the amine dosage to such a level that'a greenish color will develop in thesample at step 3' in the procedure outlined above.

I have found that-as little as one-eighth part per million of the amine compound can be detected effectively by my procedure.

In the prevention of corrosion in steam generating apparatus, other amino compounds such as ammonia, .mor pholine and cyclohexylamine are used. These are It is interesting to note that my not filming method of analysis when the copper lake is used is completely-insensitiveto ammonia, morpholine, and cyclohexylamine, but is extremely sensitive to the so-called 'longechain aminessuch as octadecylamine (C H NH ,or-any. of the compounds used in the methods disclosed in the Denman and Kahler patents. Broadly speaking, th6?.00 I P0 1C S:, are; generally represented by. the f rmula:

a -Nan nifll o m l R enot n alkyl e' j uER and represent hydrogen or an alkyl group. This formula is intended tocover theprimary, secondary, and tertiary es: when'oneghydrogen isreplac' d in NH the "rs't'iitingccm eunc-may bedesignated RNH When two hydrogens are replaced, the secondary amine is represented by RRNH and contains an imino group; and when three hydrogens are replaced, the tertiary amine is formed having the formula RR'RN.

It is well known in the art that many dyestuffs will combine with metal ions to form insoluble compounds known as lakes. The rate of precipitation or flocculation of these compounds varies considerably, although in due time the insoluble form generally comes out of solution.

It has been found. that some; combination of dyes and metal ions newly formed or formed in the presence of a stabilizing agent will not precipitate or flocculate immediately. One such dye is Eriochrome Azurol B (CI-720). Its magnesium salt can be formed without immediate precipitation and can be stabilized for long periods with polyvinyl alcohol. (Hart, J. A. and Lee, E. W., Tappi, vol. 34, No.v 2, pages 77-79, February 1951.) This stabilized or newly formed lake responds by a color change to additions of cationic soaps, particularly of the. quaternary. amine type. This combination is not responsive to long chain primary amines (filming amines) nor to other types of nitrogen compounds extensively used for corrosion control in steam and condensate systems.

By substituting other metals such as copper or zinc, for the magnesium, I have found that a stable combination of dye andmetal can be made with a clear yellow or amber color and that under the proper conditions of pH value, the lake color is markedly changed by the presence of verysmall amounts of long chain primary amine. The pH value of thetestsolutiou after all addirtions have beenmade should be between about 6.9 and about 7.2 to achieve these results. The amounts of amine detectable can be as small as one-tenth parts per million. Short chain amines and related nitrogen compounds do not give this color change. This permits a distinction to be made among the materials commonly used for steam and condensate line corrosion problems.

The action of the long chain amines in producing the color change lies largely in their efiect on the state of aggregation of the dyestufi', which in the case of the copper salt seems tobe one of true solution, or a lake stabilized by excess dyestutf. This change in aggregation can 'be seen from the fact that the test solutions after the color change will flocculate in due time. Low concentrations may remain stable for days, but test solu tions containing about one milligram of amine will flocculate in 24 hours.

If desired this flocculation can be prevented by the use of dispersing or stabilizing agents such as polyvinyl alcohol, acrylic acid polymers, etc. but for most purposes in carrying out my test procedures these agents are unnecessary.

Since at a concentration of 2.5 parts per million of amine in the sample being analyzed will produce a maximum depth of blue color, if it is suspected that the concentration exceeds 2.5 parts per million, the sample can be diluted with distilled water known to be free from the amine and the analysis is then made on the diluted sample.

Although in the foregoing procedure I have outlined a preferred method of preparing reagents which involves a natherexacting method and precise amounts ofspecific reagents, it should be pointed out that the principal objectiveisto prepare the three reagents in such a manner that the final pH value of the sample undergoing analysis is in the" working range of about 6.9 to 7.2. Hence reagent No. l is merely an acidic solution which when combined with the alkaline reagent N0. 2 yields the proper pH value. Glacial acetic acid is' prepared in reagent No. 1 but of course any mineral acid such as hydrochloric; sulfuric, nitric; orphosphoric acid'could be used instead. However, the acetic acid ismuch more amenable to buffering with the alkaline salts than are the mineral acids. With the latter, control of the pH is difiicult.

While I have mentioned two brands of azure blue dye (Azurol B in textile circles) there are other brands which are equally satisfactory. The designation CI-720 is the ofiicial color index designation of the dye.

Azurol B is chemically the condensation product of orthocresotinic acid and orthodichlorobenzaldehyde.

I claim:

l. A method of determining the presence of longchain primary, secondary, and tertiary aliphatic amines in aqueous media which comprises forming a lake of copper and Azurol B dye, adjusting the pH value of the lake to between about 6.9 and 7.2, adding thereto an aqueous media containing a long-chain aliphatic amine and observing the color of the lake.

2. A method of visually determining the concentration in aqueous media of long-chain primary, secondary, and tertiary aliphatic filming amines, which comprises adding to a measured quantity of the aqueous media a buttered solution of a lake of copper and Azurol B dye, maintaining the pH value of the resultant solution in the range of from about 6.9 to about 7.2 and thereafter colorimetrically determining the concentration of amine.

3. A method of determining the presence of longchain primary, secondary, and tertiary filming aliphatic amines containing at least eleven carbon atoms in an alkyl radical thereof which comprises reacting a buffered solution of copper and Azurol B dye at a pH of from about 6.9 to about 7.2 with a dilute solution containing less than 10 parts per million of said amine, and thereafter colorimetrically determining the concentration of amine by comparison with known color standards.

4. A method of determining the presence of a filming amine of the long-chain aliphatic type in aqueous media which comprises forming a lake of copper and Azurol B (CI-720) in an aqueous solution buffered to a pH value of from 6.9 to 7.2 whereby upon visual inspection the lake will range in color from amber yellow with no amine present through greento a deep blue With 2.5 parts per million of amine present.

5. A method of determining the presence of longchain aliphatic amines in aqueous media without interference from other types of amines present which comprises forming a lake of copper and Azurol B dye in the presence of an aqueous sample suspected of containing a long-chain aliphatic amine and observing the color of the lake.

References Cited in the file of this patent Snell Coll. Meth. of AnaL, vol. IV, 3rd ed., 1954, p. 67.

Hart et al., Tappi, vol. 34, February 1951, p ps. 77-9.

Feigl Chem. of Spec. Sel. and Sensitive Reaction, 1949, p. 217.

Feigl Chem. Spec. Sel. and Sens. React., 1949, p. 544. 

1. A METHOD OF DETERMINING THE PRESENCE OF LONGCHAIN PRIMARY, SECONDARY, AND TERTIARY ALIPHATIC AMINES IN AQUEOUS MEDIA WHICH COMPRISES FORMING A LAKE OF COPPER AND AZUROL B DYE, ADJUSTING THE PH VALUE OF THE LAKE TO BETWEEN ABOUT 6.9 AND 7.2, ADDING THERETO AN AQUEOUS MEDIA CONTAINING A LONG-CHAIN ALIPHATIO AMINE AND OBSERVING THE COLOR OF THE LAKE. 